Technical Field
The present invention relates to an engine starting apparatus.
Related Art
A conventional technique for starting an engine uses an inertia-engagement-type starter to crank the engine until a predetermined revolution speed of the engine NO within a low engine-speed range (5400 rpm) is reached, and after the revolution speed of the engine NO is reached, increases the revolution speed of the engine to an idle speed with combustion in a combustion chamber. Usually, as shown in FIG. 4, increasing the revolution speed of the engine to the idle speed requires multiple fuel injections and ignitions (multiple fuel injections in the case of the diesel engine). For example, first fuel injection and ignition, second fuel injection and ignition, third fuel injection and ignition, and fourth fuel injection and ignition are sequentially performed in a first cylinder, a third cylinder, a fourth cylinder, and a second cylinder, respectively.
As for the combustion in the combustion chamber, an ideal fuel injection quantity in terms of the exhaust emission and fuel economy decreases with increasing revolution speed of the engine. A fuel injection quantity in excess of the ideal fuel injection quantity will cause rich combustion or in-cylinder injection of excess fuel, which leads to poor fuel economy and deteriorated exhaust emission. Therefore, it is desired to predict a revolution speed of the engine at ignition, more specifically, at firing in the case of the gasoline engine or at fuel injection in the case of the diesel engine, and set a fuel injection quantity corresponding to the predicted revolution speed of the engine.
For the gasoline engine, the fuel injection quantity is set, which is followed by injecting the set quantity of fuel and firing the injected fuel. Therefore, it is desired to predict a revolution speed of the engine at firing and set a fuel injection quantity corresponding to the predicted revolution speed of the engine.
The above conventional technique, however, necessitates multiple ignitions until the idle speed is reached. In addition, as described below, it is very difficult to predict the revolution speed of the engine at each ignition timing.
When a first combustion does not take place at the first ignition, the starter continues to crank the engine through application of a torque to the engine. Therefore, the second ignition takes place during cranking of the engine, that is, while the revolution speed of the engine is in a low revolution speed range.
When a first combustion takes place at the first ignition, the cranking of the engine terminates under action of a one-way clutch of the starter, and the revolution speed of the engine increases with the combustion. The second ignition takes place during increasing of the revolution speed of the engine through the combustion, which leads to a reduced fuel injection quantity as compared with when the first combustion does not take place at the first ignition.
The fuel injection quantity at the second ignition is set prior to the second ignition timing. However, at the time when the fuel injection quantity at the second ignition is set, it is not known whether the first combustion has taken place at the first ignition. Therefore, it becomes difficult to accurately predict the revolution speed of the engine at the second ignition.
Conventionally, as a failsafe, the fuel injection quantity at the second ignition is set to a slightly larger fuel injection quantity without predicting the revolution speed of the engine at the second ignition so that the larger fuel injection quantity can cause the second combustion even in the absence of the first combustion at the first ignition. Such a conventional technique suffers from poor fuel economy and deteriorated exhaust emission when the first combustion takes place at the first ignition.
In addition, predicting the revolution speed of the engine at ignition after termination of the cranking of the engine necessitates predicting a rate of increase in revolution speed of the engine resulting from the combustion, which makes it difficult to predict the revolution speed of the engine at ignition after termination of the cranking of the engine. That is, it is difficult to predict the revolution speed of the engine during a time period from when the predetermined revolution speed of the engine NO (in the low revolution speed range) is reached at which the cranking of the engine is terminated to when the idle speed is reached. Since the revolution speed of the engine at ignition is thus likely to be underestimated, the fuel injection quantity will be inevitably overestimated, which causes revolution speed of the engine overshoot above the idle speed, as shown in FIG. 4.
That is, with the conventional technique for starting the engine, it is very difficult to predict the revolution speed of the engine at ignition during increasing of the revolution speed of the engine, which inevitably leads to control such that the revolution speed of the engine at ignition is underestimated and the fuel injection quantity is therefore overestimated. This may lead to the revolution speed overshoot in excess of the idle speed, poor fuel economy, and deteriorated exhaust emission.
Japanese Patent No. 4973595 discloses a technique for correcting an initial fuel injection quantity. This technique, however, does not disclose accurately predicting the revolution speed of the engine at ignition to set a fuel injection quantity corresponding to the predicted revolution speed of the engine. In addition, Japanese Patent No. 4973595 does not disclose setting a fuel injection quantity corresponding to the revolution speed of the engine at ignition while the revolution speed of the engine is increased.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an engine starting apparatus capable of accurately predicting a revolution speed of an engine at ignition and injecting an appropriate quantity of fuel to increase the revolution speed of the engine to an idle speed.